The present invention relates to a method and apparatus for controlling the heat input to a dryer and, more specifically, to controlling the heat input in an energy efficient manner.
Typically in dryers known in the art, full heating energy is applied to a clothes treatment chamber throughout a drying cycle up to a point in time when the moisture content of the clothes is reduced below a threshold level. At this point or a predetermined time period thereafter, the drying energy is terminated and the drum of the dryer continues to rotate for a predetermined amount of time to allow cooling of the clothes treatment chamber. When a sufficient time to allow cooling or after a cool down temperature has been reached, the dryer is then shut-off. Alternatively, it is also known in the art to simply maintain an exhaust temperature of the dryer at a set temperature level after an initial period of heating from the start of the drying cycle for a predetermined time period.
However, it has been discovered by the Applicants that efficient drying of clothes (i.e., moisture reduction) does not necessarily require that the power level of the heating element or the exhaust temperature of the dryer be maintained at a set level. Rather, the Applicants have found through testing that moisture retention of clothing within the dryer declines at a relatively constant rate even when the applied heating energy or the exhaust temperature is reduced after an initial full energy heating period of approximately 5 to 30 minutes at the start of the cycle. Accordingly, dryers known in the art that maintain a set power level or exhaust temperature are not energy efficient since full energy or exhaust temperature is not necessary to reduce moisture at a constant rate.
Thus, there is a need for an energy efficient control of drying energy that benefits from the discovery of effective moisture reduction at a constant rate with less than maximum drying energy or exhaust temperature.